The present invention relates to a method for fabricating multi-layered films used in materials and devices such as semiconductor light emitting devices as exemplified by surface emitting semiconductor lasers, various light receiving devices, and waveguide materials. In particular, the present invention relates to a method for fabricating distributed reflection multi-layered film mirrors (DBR mirrors).
A distributed reflection multi-layered film mirror (DBR mirror) consists of laminated layers in which materials having different refractive indices are periodically alternated in thin films. The optical thickness of each thin film is made to be xc2xc of the wavelength of the generated light. An example of such a DBR mirror achieves a reflectance of 99% or higher when it is made of 10 to 20 layers (5 to 10 pairs of layers). As an example, a pair of DBR mirrors having such properties are provided to sandwich a thin film active layer in a device such as a surface emitting semiconductor laser.
These DBR mirrors are ordinarily fabricated by forming a plurality of thin films in a continuous manner using methods such as vacuum evaporation, sputtering, thermal CVD, and vapor phase epitaxy, in which the vapor of the materials making up the thin films are condensed/solidified on a substrate (in other words, a vapor phase film growth method).
However, in a vapor phase film growth method, materials making up the thin films may thermally decompose at the evaporation temperature of the thin film materials. Moreover, in cases where thin film materials contain a plurality of atomic elements, it is necessary, for example, to provide an evaporation source for each element in order to grow thin films made of uniform compounds, or compounds without compositional variation along the film thickness direction. This is because the vapor pressure differs for each element. Thus, an apparatus tends to be complicated and large.
Moreover, patterning techniques for DBR mirrors, in particular fine patterning techniques, are important in order to fabricate devices such as various active devices and low-loss optical waveguides. When a vapor phase film growth method is utilized to form desired arrangement patterns of thin films, it is necessary in general to combine and/or repeat basic processes such as thin film formation, photoresist application, photomask alignment, lithographic exposure, photoresist development, etching, cleaning and so forth. This overall process requires many basic processes and becomes very complicated.
Furthermore, when thin films forming a DBR mirror of multiple layers are fabricated, as an example, by a conventional sputtering method, a mechanism becomes necessary which exchanges (switches) targets for each of the multiple layers, thereby making an apparatus complicated. Hence, problems arise in that manufacturing cost is high and the yield is low.
Moreover, it is possible to create differences in the crystal growth rate on certain different areas on a substrate, and to form patterns of thin films. This creates a DBR mirror having different wavelength properties for the different areas on the substrate. However, in this method, it is very difficult to change the crystal growth rate abruptly between fine areas. Hence, it has a limit in providing a DBR mirror having different wavelength properties in different fine pattern areas.
The object of the present invention is to provide methods for fabricating distributed reflection multi-layered film mirrors, wherein the fabricating methods allow the formation of arrangement patterns of thin films with ease and in a short amount of time, and wherein a set of laminated thin films having fine patterns can be obtained with high reliability by the fabrication methods, and wherein the fabrication methods provide easy control over the film design, such as film thickness and reflection properties such as reflectance.
The present invention provides methods (1) to (15) for fabricating distributed reflection multi-layered film mirrors described below.
(1) A method for fabricating distributed reflection multi-layered film mirrors having a plurality of laminated thin films, each with a different refractive index, wherein the thin films are formed using a liquid phase film formation method.
(2) The method for fabricating distributed reflection multi-layered film mirrors of (1) above, wherein the liquid phase film formation method includes steps of:
applying thin film materials from which the thin films are formed, and
solidifying the thin film materials which are applied.
(3) The method for fabricating distributed reflection multi-layered film mirrors of (2) above, wherein the step of solidifying the thin film materials is performed before different thin film materials are applied on the thin film materials.
(4) The method for fabricating distributed reflection multi-layered film mirrors of (2) above, wherein after a plurality of layers of the thin film materials in their intermediate solid states are laminated, they are solidified.
(5) The methods for fabricating distributed reflection multi-layered film mirrors of one of (2) through (4) above, wherein solidification of the thin film materials is performed using thermal processing.
(6) The method for fabricating distributed reflection multi-layered film mirrors of one of (1) through (5) above, wherein composite materials forming thin films are the dielectric materials.
(7) The method for fabricating distributed reflection multi-layered film mirrors of one of (1) through (6) above, wherein the liquid phase film formation method utilizes an ink jet method.
(8) A method for fabricating distributed reflection multi-layered film mirrors in which at least two distributed reflection multi-layered film mirrors having a plurality of laminated thin films, each with a different refractive index, are arranged on the same surface, wherein the formation of thin films forming each of the distributed reflection multi-layered film mirrors is performed using a liquid phase film formation method having a step of applying thin film materials which form the thin films in patterns, and a step of solidifying the thin film materials.
(9) The method for fabricating distributed reflection multi-layered film mirrors of (8) above, wherein the liquid phase film formation method utilizes an ink jet method.
(10) The method for fabricating distributed reflection multi-layered film mirrors of (8) or (9) above, wherein the application of patterns of the thin film materials is performed so that two or more of the distributed reflection multi-layered film mirrors which are arranged on the same surface are formed in a parallel manner.
(11) The method for fabricating distributed reflection multi-layered film mirrors of one of (8) through (10) above, wherein two or more of the distributed reflection multi-layered film mirrors which are arranged on the same surface have different reflection properties from those of the others.
(12) The method for fabricating distributed reflection multi-layered film mirrors of one of (8) through (1) above, wherein the step of solidifying the thin film materials is performed before different thin film materials are applied on the thin film materials.
(13) The method for fabricating distributed reflection multi-layered film mirrors of one of (8) through (11) above, wherein after a plurality of layers of the thin film in their intermediate solid states are laminated, they are solidified.
(14) The method for fabricating distributed reflection multi-layered film mirrors of one of above (8) through (13) above, wherein solidification of the thin film materials is performed using thermal processing.
(15) The method for fabricating reflection multi-layered film mirrors of one of (8) through (14) above, wherein composite materials forming the the thin films are dielectric materials.